march 11, 2010 11:23am

Actual space heating revisited

A few entries back I presented numbers for January and February that show the amount of space heating we actually used compared to the PHPP predictions. I think a bit more explanation is due.

After checking average temperatures of a third weather station in the region, and re-crunching the numbers, my calculations do seem correct.

The explanation for the seemingly low space heeat numbers is fairly simple (I think):
1) Our PHPP certification is based on "Standard" internal heat sources (as calculated by PHPP for our house and usage).
2) Our climate model has long term averages for temperature and insolation which do not include a 30-year cold period like 2009-2010.

For the adjusted percentages of 88% and 80% I switched to "PHPP-Calculation" which only includes our actual appliance usage. A few months ago our trusty 20+year-old Bosch washing machine stopped working. We are still using our fantastic cold larder for all fresh food storage, and we do not have a fridge or freezer. Our only mostly-on appliance is a laptop and speakers that use <50W. Consequently our PHPP calculated space heat requirements increase.

In addition I have only considered the actual mean temperatures and do not have actual insolation data to enter into PHPP. I believe that February in particular produced higher insolation levels than our PHPP climate model indicates.

Taking the above into consideration I think our actual space heating for January and February may be 5-10% less than general predictions. But whatever the future holds it does show how well the house is already performing... and what an excellent tool PHPP is for low-energy house design.

Posted By: MarkTiramani

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march 08, 2010 11:10am

What wonderful weather

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One of the three neighbouring buzzards that roost just above the house.

The last 5 or 6 days have been quite sunny and today is exceptional. Cold nights but 20-25°C indoor temperatures and more bath-loads of solar hot water than any self respecting brit would have time for.

It is an indescribabley joyous feeling at Y Foel when the sun, the wildlife and the house resonate with such energy.

Posted By: MarkTiramani

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march 08, 2010 10:55am


Nice to meet a few familiar faces, and to put a couple of faces to names.

But for the rest of the show: Much busier than I remember from my last visit a few years ago, but is this just the new gold rush? Do more than 20% of exhibitors actually believe in the "eco" credentials of their products?

Posted By: MarkTiramani

1 comments | Comment

march 03, 2010 10:40am

The results are in, the jury is out...

It was surely an achievement to be awarded Passivhaus certification, but to me it only has any lasting merit if monitoring supports the calculated performance.

A new build can take 6 months to fully dry out and settle, even with a conventional heating system, so I had not really expected to have definitive measurements until this time next year.

However, this winter has been the coldest (and wettest) in the last 30 years. It seems obvious that if our actual space heating requirements for recent months were low enough it would at least prove the cold weather performance.

Multi-room monitoring is not up and running yet but I do now have 24/7 temperature and relative humidity data logged from mid January onwards. The indoor sensor is located in the main open-plan living area. I have 5 other thermometers located in different rooms for my manual records. These determined the location of the 24/7 logging sensor. Comparing measurements show that the logged data is reliable and a very fair reflection of the overall temperatures in the house.

I also found another local weather station that gives a good comparison with my outdoor temperature and humidity readings:

The climate model used for our PHPP calculations is a triangulation of 3 meteo stations, 2 in Wales and one in England. It is of course based on long term monthly averages, and winter 2009-2010 has been a long way away from the November-February averages.

So, what is the conclusion so far:

Adjusting for actual mean temperatures, Y Foel used:
January: 88% of the kWh predicted by PHPP for space heating.
February: 80%

More on this soon I hope...

Posted By: MarkTiramani

19 comments | Comment

march 02, 2010 12:01pm

Energy usage decreasing

May 1st brought the first decrease in the average daily primary energy (PE) consumption since last autumn.

The total for the day was 11.4kWh. The average is now at 17.1kWh per day.

This was the sunniest day for months. The earth blocks and slate floor charged up nicely. The core temperature of the blocks increased roughly 1°C to over 20°C.

Today, 2nd March, is also very sunny. 6/8 cirrus so we have just reached 23.7 indoors at midday.

Posted By: MarkTiramani

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february 24, 2010 10:33am

Euro Fighter on roof?

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So what's so interesting about 2 inches of snow on a roof? Parts of the UK will have had 5 times as much as we did this winter.

Well, there are quite a few low level training flights in the valley, from RAF Valley, and they occasionally come right over our hill from the west on a predictable flight path.

The house is, like many PH I imagine, very sound proof. With all doors and windows closed only the loudest of noises get past the sound of my keyboard. The lowest jets sound relatively loud, but nothing like the noise when heard from inside a conventional timber frame or bricks and mortar structure.

Three days after recent snow, and long after it had apparently all melted away, we were slightly startled by the sound of a jet flying overhead, but it did not appear rushing off to the east where it should have been, and the sound was brief and unusually truncated. We looked at each other and as ususual I jumped to a conclusion and rushed out saying that "something has come down", meaning a tree or the like.

It was only when I climbed the bank behind the house that I realised the sound must have come from a large patch of snow sliding off the north facing roof slope.

This got me thinking: Designers try and align PH facing due south, with the south facing roof pitch sometimes being influenced by the fitting of solar collectors or tiles. However, the north slope might be designed with a shallower pitch to accommodate a living roof etc. PH roofs are so well insulated that snow accumulation is more likely, even on a 35-40° slope, than on a conventional building. Could this become a potential issue if UK winters become more extreme?

Just wondered...

Posted By: MarkTiramani

1 comments | Comment

february 20, 2010 11:58am

Spring frogs

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Frogs can't be wrong can they?
Well they're not taking any chances and have decided to submerge themselves in the leaves at the bottom of the pond again.

Winter seems very determined to have its say this year.

What happens if you design and certify a Passivhaus for one climate model and then someone cocks up the delivery and you get the model for someone else's house?

Posted By: MarkTiramani

7 comments | Comment

february 18, 2010 12:09pm

PH supply air heating misunderstood?

Are we in danger of misunderstanding and misinterpreting the implementation of supply air heating in Passivhaus projects in the UK?
(Or is it me misinterpreting the writings of others?)

I think we may be confusing the heating potential of air supplied by an MVHR with the kind of supply air heating found in office buildings and the like via conventional HVAC systems. The supply air rates are very different.

The supply air volume in a PH is relatively small: 0.3-0.5 ach. There is virtually no infiltration via vents, doors, windows or building fabric.

For short term, rapid response heating:
Pump through enough hot air to raise the general indoor temperature by just 1°C within 1 hour and the relative humidity will drop to an unacceptable level. Most MVHRs would struggle to supply the volume required anyway.

At Y Foel we have nearly a full winter's practical experience with this. After many experiments and measurements I believe I have a reasonable handle on it.

Also, the 55°C scorched dust, smelly air problem may be a red herring. I am aware of several supply air heating methods available for installation in the ducting of PH ventilation systems:
Hot wire elements.
PTC (Positive Thermal Coefficient) elements.
Fluid based heat exchangers.

All 3 introduce a degree of air flow resistance.
To compensate and reduce the risk of unwanted pressure differentials the heating elements are either:
Significantly overdimensioned
Permit varying degrees of bypass circulation around rather than through the element.
or both.

I can only test what we have here of course, but I suspect that space restrictions and air supply rates will in practice determine results not too dissimilar to the following:

MVHR air exchange rate: 85m­³/h
PTC mounted immediately post MVHR consumes 500W
160mm ducting at MVHR:
Temperature at centre of duct 50mm above the PTC element: 64°C
Temperature at outer 20mm of duct 50mm above PTC element: 22°C
Average temperature of supply air as it exits 5 vents: 28.7°C

We have an F7 filter (as do most PH MVHR systems?) pre MVHR, as well as the built-in dust filters. How must dust is likely to hit the heating element? In our case virtually none. If it did the PTC element with a surface temperature much greater than 60°C would certainly cause scorching and odours.

How many of the above PH air supply heating units are actually capable of delivering 50°C supply air to rooms?

Posted By: MarkTiramani

765 comments | Comment

february 18, 2010 08:23am

Shut that door!!

We had an old friend visit yesterday @ 6PM and we rapidly fell into debate, solving world issues and the like. But after a couple of hours I glanced at the indoor temperature and wondered for a moment why it was low'ish. With 3 adults, rather than the usual 2, we normally do not need any supplementary heating.

After another hour or so I started to wonder why the temperature had not climbed above 19.9°C, despite about 1.2kW of electric heating. I looked in the hall and found both the front door and the porch door were open. Not wide, just 1 and 2 inches respectively, but enough to pretty much bugger up the whole air-tight-Passivhaus principle :)

Posted By: MarkTiramani

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february 18, 2010 08:15am

Market day: Congratulations Shirley :)

After what seems like years of ideas and planning Shirley at last got a chance to share her culinary delights with the unsuspecting Machynlleth public.

Indian-based vegetarian dishes to take home: Would there be any demand? Yes, Shirley sold out by 11:45AM! She only made a small number of portions for a sort of test run.

It was a huge relief after a lot of hassle in recent months/years. One of the best days I can remember... Well done Shirley :)

Posted By: MarkTiramani

1 comments | Comment